Sitagliptin is commercialized as a phosphate salt and is chemically known as (R)-4-oxo-4-[3-(trifluoromethyl)-5,6-dihydro[1,2,4]triazolo[4,3-a]pyrazin-7(8H)-yl]-1-(2,4,5-trifluorophenyl)butan-2-amine phosphate monohydrate. This salt has the following structure:

Sitagliptin is a drug used in the treatment of type 2 diabetes mellitus and belongs to the gliptin group. Sitagliptin is a white, crystalline, slightly hygroscopic solid, which is easily manipulated; its structure has a chiral center consisting of a primary amino group.
Its mechanism of action is related with the inhibition of dipeptidyl peptidase (DPP-4), which allows increasing incretin hormones GLP-1 and GIP that control insulin and glucagon release from the pancreas.
On the other hand, the application of crystal engineering has been described as a tool for providing a viable alternative to enhance the physicochemical properties of drugs without modifying their chemical structure. The physicochemical properties of the active pharmaceutical ingredients and the bulk materials can be modified, maintaining the intrinsic therapeutic activity of the molecule (Yadav A., et. al. Co-Crystals: A Novel Approach to Modify Physicochemical Properties of Active Pharmaceutical Ingredients, 2009).
The aforementioned is based on the ability of a molecule to exist in two or more solid forms, which differ in the spatial distribution of the atoms or molecules.
As a result of the spatial arrangements of the atoms or molecules, the solids have different physical and chemical properties, which modify the chemical stability, thermal stability, density, hardness, hygroscopic tendency, flow rate, absorption rate (bioavailability) or the behavior of a compound in suspension, and therefore, the final pharmaceutical product.
In the prior art, several crystalline forms of sitagliptin salts, as well as processes for their preparation, have been described. Specifically, document U.S. Pat. No. 6,699,871 B2 describes a process for preparing sitagliptin base and its hydrochloric salt; whereas U.S. Pat. No. 7,326,708 discloses a crystalline form of sitagliptin phosphate monohydrate and a process for preparing the same.
Document EP 2318411 A2 is directed to crystalline salts of sitagliptin with a monobasic, dibasic or tribasic acid, whereas WO 2005/072530 discloses sitagliptin salts and hydrates thereof, wherein the acid addition salt is selected from the group consisting of hydrochloric acid, tartaric acid, benzenesulfonic acid, p-toluenesulfonic acid and 10-camphorsulfonic acid.
WO 2009/085990 and WO 2010/092090 describe crystalline forms of sitagliptin coupled with coformers selected from sulfuric acid, hydrobromic acid, methanesulfonic acid, acetic acid, benzoic acid, oxalic acid, succinic acid, mandelic acid, fumaric acid, D-glucuronic acid, L-lactic acid, malonic acid, citric acid, crotonic acid, ascorbic acid, among others.
WO 2013/054364 A2 refers to solid forms of sitagliptin, particularly to anti-oxidant acid addition salts of sitagliptin, processes for preparing the same, and pharmaceutical compositions containing said salts.
Document US 20140081026 A1 describes a process for the synthesis and industrial production of sitagliptin. In addition, US 20150051213 A1 describes sitagliptin salts with organic acids, polymorphic forms, processes for their preparation and pharmaceutical compositions thereof.
An amorphous solid is the one having particles that lack a long-range order. Amorphous solids constitute a way of increasing bioavailability of poorly soluble drugs by means of enhancing their dissolution rate and solubility (Guy Van Den Mooter, The use of amorphous solid dispersions: A formulation strategy to overcome poor solubility and dissolution rate, 2012).
In amorphous solids, the molecular energy is high and molecular mobility is higher than the crystalline state. These features provide unique physicochemical properties to amorphous solids, such as higher solubility and higher dissolution rate in aqueous media (Yihong Qiu, et. al. Developing Solid Oral Dosage Forms, 2009).
With regard to amorphous solid phases, document WO 2010/000469 discloses the preparation of an amorphous solid of sitagliptin with citric acid. Document WO 2012/131005 describes pharmaceutical compositions comprising amorphous sitagliptin, wherein the amorphous sitagliptin is prepared from a solution comprising sitagliptin and a crystallization inhibitor selected from cellulose derivates, polyvinylpyrrolidone, polyvinylpyrrolidone derivatives and/or mixtures thereof.
Document US 20140350023 A1 discloses amorphous forms of sitagliptin obtained with mandelic acid, fumaric acid, benzenesulfonic acid, methanesulfonic acid and succinic acid. Document WO 2015/114657 A2 provides amorphous forms of sitagliptin in the absence of coformers.
As mentioned above, the preparation of amorphous solids of sitagliptin has been reported; however, the coformers used in the present invention, as well as the advantages associated to their use, have not been disclosed, aside from the fact that the methods of preparation described in the state of the art are complex.
While amorphous solids possess interesting properties from the pharmaceutical point of view, such as a higher solubility, they are not usually marketed due to their lower chemical stability, higher hygroscopicity and tendency to crystallize.
For the above reasons, there is a need of having new solid phases (NSP) of sitagliptin with enhanced pharmaceutical properties, which are obtained by a simple method and which are also stable under ambient conditions.